six.raise_from not found

[jessebrennan]

Error experienced by @coverbeck.

traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "./app.py", line 644, in callback
    if whitelist_checker is not None and not whitelist_checker.is_authorized(email):
  File "/usr/local/lib/python2.7/dist-packages/bouncer/bouncer.py", line 40, in is_authorized
    return email in self.whitelist()
  File "/usr/local/lib/python2.7/dist-packages/bouncer/bouncer.py", line 47, in whitelist
    six.raise_from(SecretManagerException("The requested secret {} was not found"
AttributeError: 'module' object has no attribute 'raise_from'
[pid: 28|app: 0|req: 5/8] 172.23.0.5 () {54 vars in 1958 bytes} [Tue Sep 18 00:48:59 2018] GET /gCallback?state=VjOBHzhYbD6tBEFv6WLByP9WwouLzE&code=4/XgAdWbmvupNBwC8LdXKd_HcsXrt8wMXz_xA27sf4MC47gDDrO4TVimzcryc4vDl5ak-7CIVu7w7dzKtKS2sFYQo&scope=https://www.googleapis.com/auth/userinfo.profile+https://www.googleapis.com/auth/userinfo.email => generated 291 bytes in 651 msecs (HTTP/1.0 500) 2 headers in 84 bytes (1 switches on core 0)

This SO post makes me think that maybe some libraries are doing something funky: https://stackoverflow.com/questions/48716833/attributeerror-module-object-has-no-attribute-raise-from-for-six-library

A simple solution would be to just vendor the 'raise_from' package.